The fact that ‘Austria does not allow dual citizenship’ seems to be an absolute truth that is widely recognised by the public. However, it is not actually true: there are several possible constellations in which someone can have one (or sometimes even several) other nationalities in addition to Austrian citizenship. It is, of course, true that the acquisition of citizenship by conferral usually (but not in every case!) requires the renunciation of the previous citizenship. It is also true that in the case of the acquisition of a foreign nationality by an Austrian citizen, the ‘automatic’ loss of citizenship occurs. Apart from this, however, there are certainly cases in which someone can have other citizenships - even in addition to Austrian citizenship.
The most relevant situation in practice is the descent of parents who have different nationalities. It should be noted that this does not mean that the child unconditionally and always acquires both nationalities by descent. However, this constellation can very often lead to multiple nationalities. The same applies if the child is born in a country that recognises the country of birth principle (‘ius soli’).
However, the situation is somewhat more complex for adults. We can, for example, name descendants of former citizens who fled during or immediately after the Second World War due to persecution or were even murdered by organs of the German Reich. This group of people can acquire Austrian citizenship in accordance with § 58c StbG without having to renounce their previous citizenship.
For Austrians living abroad in particular, the authorisation to retain their citizenship is of course another possible way of acquiring another nationality. In practice, however, this is difficult to enforce and the authorities' behaviour is not always predictable.